1. Field of the Invention
The invention relates to a liquid crystal display (LCD), and more particularly to a backlight module.
2. Description of Related Art
In recent years, LCDs that have been developed toward full-color display gradually replace a conventional cathode ray tube (CRT) display and have become a main stream of displays in the market due to the advantages of a low operation voltage, non-radiation, light weight, small volume occupancy, and so forth.
The LCDs are non-self-illuminating displays, and therefore display functions of the LCDs are achieved when required light is provided by backlight modules. With increasing consciousness of environmental protection, cold cathode fluorescent lamps (CCFLs) serving as light-emitting devices in conventional backlight modules are gradually replaced by light-emitting diode (LED) devices because the LED devices are more friendly to environment. When an LED device is applied in the backlight module, e.g., an edge-type backlight module, the LED device is usually mounted on a bar-shaped printed circuit board (PCB) to form an LED light bar. The LED light bar is often electrically connected to a control circuit board through a flexible printed circuit (FPC).
FIG. 1 is a schematic top view illustrating a light guide plate (LGP) and an LED light bar in a conventional edge-type backlight module. With reference to FIG. 1, the conventional edge-type backlight module 100 includes an LGP 110 and a linear light source 120. The LGP 110 includes a top light-emitting surface 112 and a light-incident side surface 114 connected to the top light-emitting surface 112. The top light-emitting surface 112 has a peripheral region 112a and an effective illumination region 112b, and the peripheral region 112a is connected to the light-incident side surface 114. It can be learned from FIG. 1 that the linear light source 120 is configured next to the light-incident side surface 114. The linear light source 120 includes a circuit board 122 and a plurality of LED devices 124. Each of the LED devices 124 is configured on and electrically connected to the circuit board 122.
As shown in FIG. 1, a pitch between any two adjacent LED devices 124 of the linear light source 120 is P, and the shortest distance from the light-emitting surface of each of the LED devices 124 to the edge of the effective illumination region 112b is A. In order to uniformize the luminance of the effective illumination region 112b, users determine the optimal A/P ratio based on the divergence angle á of light of the LED devices 124. However, the LCD has been developed to comply with the requirement for the slim border design, and therefore the shortest distance A from the light-incident surface of each of the LED devices 124 to the edge of the effective illumination region 112b needs to be further shortened. When the A/P ratio is overly low, dark and bright hot spots are generated at the effective illumination region 112b close to the light-incident side surface 114. The dark regions shown in FIG. 1 refer to regions with low luminance. The hot spots can be removed by shortening the pitches P, while more of the LED devices 124 are required when the pitches P are shortened. As such, manufacturing costs are increased.
Accordingly, how to remove the hot spots caused by the overly low A/P ratio in compliance with the requirement for slim border design without significantly increasing the manufacturing costs now becomes an important issue to be resolved.